The present invention relates to an adhesive which is suitable for an inorganic vapor-deposited film where a thin membrane layer of inorganic oxide is formed on a plastic film. More particularly, it relates to an adhesive used for a layered product of material for packaging which is requested to have an airtight property for packaging of foods, pharmaceuticals, chemicals, medical instruments, electronic parts and the like and is requested to be easily opened when the content is taken out.
With regard to a material for packaging having a barrier property to oxygen gas, vapor, etc. and having a good preserving adaptability, various things have been developed and proposed. For example, as a film having an excellent gas barrier property, there have been known a thing where aluminum is layered on a plastic film (Japanese Patent Laid-Open No. 62/101,428), a thing where vinylidene chloride or ethylene-vinyl alcohol copolymer is coated and a thing where a thin membrane such as silicon oxide or the like is layered (Japanese Patent Publication No. 51/48,511).
Further, in recent years, there have been proposed an inorganic vapor-deposited film having such a constitution that a vapor-deposited membrane of inorganic oxide such as silicon oxide, aluminum oxide or the like is formed on a flexible plastic material and a layered material, a container for packaging, etc. using the same (Japanese Patent No. 3,070,702 and others). Particularly, an inorganic vapor-deposited film having a vapor-deposited membrane of inorganic oxide such as silicon oxide, aluminum oxide or the like shows an excellent transparency, has a high barrier property to vapor, oxygen gas, etc., an aroma-keeping property and the like and further has less problem to environment upon being discarded as compared with the conventional layered material for packaging, etc. using aluminum foil, Nylon film coated with a resin of polyvinylidene chloride type, etc. whereby there has been a big expectation for its consumption as a packaging material and others.
However, when the inorganic vapor-deposited film is subjected to extruding and laminating process, dry laminating process or the like with film, sheet or the like of other resin having a heat sealing property by which a layered material for packaging is manufactured, there is a problem that adhesive force between the inorganic vapor-deposited film and the conventional adhesive for laminate, anchor coating agent, etc. is low. As a result of lowering of the laminate strength as such, it often happens in the layered material constituting a bag that, when the outer package of the packaging bag is opened for taking out the content, a part of film and heat-sealing resin of the packaging bag is elongated and is hard to tear whereupon the content comes out at a time and is scattered.
In order to improve the above-mentioned laminate strength, there is a method where a pretreatment such as a corona treatment is carried out but, in the case of inorganic vapor-deposited film, the effect is not so much noted or, rather, the vapor-deposited layer may be damaged whereby there is a possibility of deteriorating the barrier property. As to another method, there is proposed a method where a primer composition containing a silane coupling agent or a coating thin membrane by a polyester resin composition is formed on an inorganic vapor-deposited thin membrane and then adhesion is carried out using an adhesive for laminate. However, there is a problem that the product is at least in a four-layered structure of inorganic vapor-deposited film/coating coat/adhesive/heat-sealing resin and accordingly that the cost increases as compared with a product in a three-layered structure and that is less economical.
In view of the above-mentioned circumstances, an object of the present invention is to provide an adhesive for inorganic vapor-deposited film where a direct coating on an inorganic vapor-deposited film is possible, a good adhesion is achieved when adhered together with a heat-sealing resin, etc. and the heat-sealing resin is not elongated when the packaging bag prepared by using that is torn but a good tear with a united manner is possible.
In order to achieve the above-mentioned object, various studies have been conducted and it has been found that a good adhesion is achieved when an adhesive for inorganic vapor-deposited film containing a compounded product and/or a reacted product of silane coupling agent with polyurethane resin or polyester resin having a branch in a molecule is directly coated on an inorganic vapor-deposited film and adhered with a heat-sealing resin and that, when a packaging bag prepared by using the above is torn, a good tearing property is achieved. Thus, the present invention is an adhesive for inorganic vapor-deposited film as mentioned below.
(1) An adhesive for inorganic vapor-deposited film which is characterized in containing a compounded product and/or a reacted product of polyurethane resin having a branch in a molecule with a silane coupling agent.
(2) The adhesive for inorganic vapor-deposited film mentioned in (1), wherein the branch concentration of the polyurethane resin is 30-300 equivalents/ton.
(3) The adhesive for inorganic vapor-deposited film mentioned in (1) or (2), wherein the polyurethane resin contains 15-95% by weight of polyester polyol component having a glass transition temperature of 30xc2x0 C. or higher when the total weight of the polyurethane resin is 100% by weight.
(4) An adhesive for inorganic vapor-deposited film which is characterized in containing a compounded product and/or a reacted product of polyester resin having a branch in a molecule with a silane coupling agent.
(5) The adhesive for inorganic vapor-deposited film mentioned in (1)-(4), wherein the silane coupling agent has an amino group.
(6) The adhesive for inorganic vapor-deposited film mentioned in (1)-(5), wherein a crosslinker of an isocyanate type is further compounded therewith.